1. Field of the Invention
This invention relates to electromagnetic radiation shielding and is more particularly concerned with containers fabricated from non-conductive materials and provided with a conductive metal layer on the inner and/or outer surface thereof and with novel methods of producing such containers.
2. Description of the Prior Art
It is generally necessary to provide means for shielding radio equipment and like equipment emitting electromagnetic radiations to prevent or attenuate the radiation being emitted. Indeed the FCC regulations require that certain categories of electronics and computer equipment be enclosed by radio-frequency interference shields.
Such shields generally comprise electrically conducting metal layers on the interior and or exterior surfaces of the enclosure for equipment which is the source of the radiation to be shielded. The metal coating can be applied by any of a variety of techniques such as brushing, spraying, vacuum metallization, electroless metal plating, adhering of metal foil and the like. One of the preferred techniques comprises electroless plating of metals on the surface of the enclosure. However, not all materials from which the enclosures are fabricated are susceptible to being plated in this manner. Thus many materials need careful surface preparation prior to electroless plating and, in some instances, the plating has a tendency to peel off or otherwise become loosened during the working life of the equipment. This is particularly so in the case of some plastic materials such as polycarbonate which are now being utilized in the fabrication of enclosures.
Illustrative of previous methods of preparing enclosure for shielding electromagnetic radiation, particularly that of radio frequency, is that shown in Waggoner U.S. Pat. No. 4,514,586 which describes electrolessly plating a layer of copper on an enclosure and then electrolessly plating the copper layer with a layer of a second metal such as nickel, cobalt and gold to protect the copper layer from deterioration due to oxidation. The process is illustrated using ABS as the substrate material and an elaborate procedure is described for pretreatment of the surface of the ABS prior to plating.
Narcus U.S. Pat. No. 4,169,171 describes a process of producing a decorative, metallized finish on an ABS substrate by a similar process to that described in the aforesaid Waggoner U.S. Pat. No. 4,514,586.
Cassat U.S. Pat. No. 4,590,115 describes the preparation of a plastic article having a decorative, metallized surface on at least one side thereof. The article is molded into the desired shape using a thermoplastic or thermoset resin having a high density of metal oxide particles uniformly suspended therein. At least one surface of the article is then subjected to the action of a chemical reducing agent to form a layer of free metal particles on said surface and additional metal is then electrodeposited on the surface which has been made electroconductive by the reduction step. The U.S. Pat. No. 4,590,115 summarizes the methods previously employed, particularly in fabrication of printed circuits, to introduce metallized patterns in selected areas of a substrate by first coating the areas in question with a suspension of cuprous oxide or other related metal derivatives in a curable resin, reducing the cuprous oxide or other metal derivative to free metal and then applying additional copper to said selected areas by electroless plating techniques.
It has not been suggested previously that means for shielding electromagnetic radiation, particularly such means obtained by fabrication from non-conductive plastic materials, could be derived readily utilizing a coating of a conductive metal which has not been applied directly to the non-conductive substrate but which has been applied after first coating the substrate surface with a suspension of cuprous oxide or like non-conductive metal in a curable resin, followed by reduction to free metal of at least the particles in the surface of said coating.
As will be described in detail hereinafter, significant advantages have been found to flow, both in terms of ease of processing and properties of the resulting product, from the use of such an approach.